Telescopable steering shafts for motor vehicles are known, in the case of which an inner spindle and an outer spindle which is complementarily arranged coaxially to the inner spindle are provided, which are telescopable relative to one another. In this manner, a position-adjustable steering column can be realized in motor vehicles, by means of which the steering wheel position can be adapted, at least in axial direction of the steering shaft, to the respective driver position in order to correspondingly improve the ergonomics for the driver of the motor vehicle and thus the safety. Telescopable steering shafts are known, furthermore, for safety steering columns in the case of which the steering shaft in the event of a crash is shortened or yields, for example in that the driver impacts the steering wheel and then pushes the steering wheel back together with the steering shaft.
Telescopable steering shafts are employed in motor vehicles between the steering gear and the steering wheel and, in addition to the position adjustment and crash safety, serve to also offset minor changes of the spacing between the steering gear and the steering column, which for example occur because of dynamic loads in driving operation through the corresponding twisting of the chassis, but also through movements of the steering gear in a rubber mounting. These minor changes of the spacing are to be offset by the telescopable steering shaft with as little noise as possible and should not be noticed by the driver.
Such a telescopable steering shaft can for example be designed as steering spindle in a steering column and/or as steering intermediate shaft between the steering spindle and a steering gear.
In addition to a smooth and non-jerking axial adjustment, the steering shaft with the telescope mechanism is to also provide as hysteresis-free as possible a transmission of the steering torque between the inner spindle and the outer spindle so that the driver on the one hand cannot detect any difference between a steering deflection into the one direction and a steering deflection into the other direction, and on the other hand any play during the transmission of the torque between the inner spindle and the outer spindle is not noticed by the driver.
In order to make available to the driver as good as possible a shifting sensation when telescoping the steering shaft for adjusting the steering wheel position it is desirable to reduce or largely avoid in particular a stick-slip effect, that is an initial sticking and sudden breaking-away of the parts relative to one another in order to make possible a fluid and low-noise adjusting of the position of the steering wheel. In addition, noises which are generated by the introduction of vibrations in driving mode are to be reduced or avoided in this way. Even for this reason, the stick-slip effect is to be reduced or avoided, by way of which because of the frequent breaking-away during the introduction of vibration while driving noises can likewise develop.
In this regard, sliding sleeves are known from the prior art which are arranged between the inner spindle and the outer spindle and which serve in order to reduce the friction between the inner spindle and the outer spindle during telescoping. Such a sliding sleeve is known for example from WO2010/037509 A1, which represents a sliding sleeve with permanently improved sliding characteristics.
From JP 2005-180631 A a sliding shaft connection is known, in the case of which a spline system applied to the inner shaft comprises splines with two different geometries, so that in the load-free state, i.e. without generating a steering moment, not all splines are in engagement with the outer shaft. These different spline system geometries on the inner shaft are highly elaborate to produce and require particularly high tolerance accuracies.
From EP 2 090 493 B1 a vehicle steering shaft and a vehicle steering device are known, in the case of which elastic connecting elements are glued into grooves of the inner shaft which extend in the shaft direction. Such a steering shaft also requires elaborate production.